This invention relates to a method for making N,Nxe2x80x2-bis(2-hydroxybenzyl)-ethylenediamine-N,Nxe2x80x2-diacetic acid (HBED). The invention also relates to a method for making the cationic salts of HBED, particularly the mono-cationic salt such as the mono-sodium salt.
Until the discovery of the mono-sodium salt of HBED and its unique properties as a subcutaneously or intravenously injectable solution (see for example PCT International Application No. PCT/US 99/02388 filed Feb. 3, 1999), a commercially useful method for making the compound, per se, was not known. While the PCT Application discloses the compound and a method for making it, there has been no direct route to make HBED or its cationic salts, e.g. the mono-sodium salt. Generally, HBED is available commercially as the mono hydrochloride salt or the dihydrochloride salt. Thus, in order to form the mono-cationic salt, the mono- or di-acid had to be neutralized and then carefully titrated to form the mono-cationic salt. When the desired active material was the mono-cationic salt, it would have to be extracted from the significant amount of sodium chloride that was formed from the dihydrochloride. The process of the invention described herein avoids the salt formation and provides a way to make HBED neat, which can then be converted to a cationic salt using a base such as sodium hydroxide.
One aspect of the invention is a process of forming N,Nxe2x80x2-bis(2-hydroxybenzyl)-ethylenediamine-N,Nxe2x80x2-diacetic acid (HBED), which process comprises hydrolyzing a compound of Formula (3) as shown in the reaction sequence I, preferably, using a weak acid in an aqueous environment. Preferably, the compound of Formula (3) is formed by reacting a compound of Formula (2) with at least two molar equivalents of the t-butyl ester of a 2-haloacetic acid. The compound of Formula (2) is shown in reaction sequence I as well.
Another aspect of the invention is the process wherein the compound of Formula (2) is prepared by reducing the compound of Formula (1) which is represented in the reaction sequence as well.
Another aspect of the invention is a process for forming the mono-cationic salt of HBED by reacting one molar equivalent of an organic or inorganic base with HBED itself.
This invention is a method for making HBED and its mono- or di-cationic salts. These are referred to as xe2x80x9ccationicxe2x80x9d salts with reference to the presence of a cation (positive) entity shown as xe2x80x9cMxe2x80x9d in formula (5). The essence of the process is the hydrolysis of the diester of HBED to form HBED itself. By reacting HBED itself with the appropriate molar quantity of a base such as sodium hydroxide the corresponding cationic salt (preferably the mono-cationic salt) is formed. The overall sequence, which starts from readily available starting materials can be seen in reaction sequence I.
Reaction sequence I is as follows. 
In reaction sequence I and throughout the specification, certain abbreviations are used as follows:
C=centigrade
DCM=dichloromethane (methylene chloride)
DMSO=dimethyl sulfoxide
EtOH=ethanol
gal=gallon
IPA=isopropanol
Kg=kilogram
L=liter
MeOH=methanol
mg=milligram
ml=milliliters
MOH=akaline hydroxide (M+=monocation)
NaBH4=sodium borohydride
THF=tetrahydrofuran
TLC=thin layer chromatography
In the first Step A, ethylenediamine (available from Sigma, P.O. Box 14508, St. Louis, Mo. 63178) is reacted with 2 molar equivalents of o-hydroxybenzaldehyde (also available from Sigma as salicylaldehyde) in a suitable solvent such as an alkanol, particularly ethanol or EtOH/5% IPA, to form the compound of Formula (1). Generally this is carried out at a temperature of about 0xc2x0 C. to about 20xc2x0 C. with cooling, as the reaction is exothermic. Generally the pressure will be about atmospheric with the reaction taking place under an atmosphere of a non-reactive gas such as nitrogen. The reaction time will generally be about 5 to about 24 hours, at least about 16 hours.
In the second Step B, the compound of Formula (1) is reacted with a reducing agent to hydrogenate the double bonds to form the compound of Formula (2). Generally, this is done with sodium borohydride in a suitable solvent or solvent mixture. A suitable solvent is, e.g., a mixture of ethanol (e.g. denatured), methanol, and tetrahydrofuran (THF). Alternatively, a mixture of THF and EtOH/5% IPA may be used. The solvent is present in a quantity sufficient to dissolve compound (1) and the sodium borohydride. The ratio of THF to the other component will be about 2:1 to about 5:1. This step is carried out at a temperature of about 0xc2x0 C. to about 50xc2x0 C., preferably less than 30xc2x0 C. Generally the pressure will be about atmospheric with the reaction taking place under an atmosphere of a non-reactive gas such as nitrogen. The reaction time will generally be about 10 to about 20 hours.
In Step C, once the compound of Formula (2) is prepared, it is reacted with at least 2 molar equivalents, e.g. 2.1, of tertiary butyl ester of a haloacetic acid, e.g. bromoacetic acid. This is done in the presence of a weak base such as potassium carbonate and an organic solvent such as DMSO. It may be useful to include t-butyl ammonium bromide. This results in the tertiary butyl ester of HBED that is shown as Formula (3) in reaction sequence I. This step is carried out at a temperature of about 10xc2x0 C. to about 50xc2x0 C. and atmospheric pressure. Other useful solvents include, e.g., chloroform. The reaction time will generally be about 10 to about 100 hours, preferably about 40 to 48 hours.
In Step D, the resulting ester is then hydrolyzed with a weak acid, such as formic acid, in a non-aqueous environment to give the compound identified as Formula (4), which is HBED itself. This step is carried out at a temperature of about 20xc2x0 C. to about 65xc2x0 C. and atmospheric pressure. The reaction time will generally be about 10 to about 100 hours, generally less than 50.
In Step E, HBED is then reacted with one molar equivalent of an organic or inorganic base to give the cationic salt, e.g. the monocationic salt shown as Formula (5) in Step E. The pharmaceutically acceptable monocationic salts prepared in accordance with the process of this invention are preparable from an inorganic or organic base. The salt derived from inorganic bases include, but are not limited to, the cations sodium, potassium, lithium, and ammonium. These are readily obtained from the corresponding hydroxides. Salts derived from organic bases include, but are not limited to, salts of primary, secondary, and tertiary amines; substituted amines including naturally-occurring substituted amines and cyclic amines. These include methylamine, ethylamine, isoproplylamine, trimethylamine, triethylamine, tripropylamine, ethanolamine, 2-dimethylaminoethanol, tromethamine, lysine, arginine, histidine, caffeine, procaine, hydrabamine, choline, N-alkylglucamines, theobromine, purine and the like. The mono-sodium salt and the mono-ammonium salt are the two compounds that are particularly preferred. This step is carried out at a temperature of about 2xc2x0 C. to about 50xc2x0 C. (preferably about 40-45xc2x0 C.) and atmospheric pressure. The reaction time will generally be about 1 to about 5 hours, e.g. about 1.5 to 2.5 hours.
As pointed out in PCT Application No. PCT/US99/02388, the HBED mono-cationic salts are particularly useful for treating iron overload by subcutaneous injection.